December 28, 2008

Questions Answered

Some questions recently appeared in the comments of these two posts, regarding energy policy.

"Fortunately" after a tragic lab mishap involving Mentos, one member of the Brickmuppet's crack team of science babes is now ideally equipped to deal with comment threads that have returned from the dead! She now shambles up to answer these questions.

First up, 'Alternate Energy' asks about the relative energy yields of sugar beets and switch grass.

That's a hard one to figure as there are several factors involved, but some ballpark assumptions can be made.

Here sugar beets are credited with providing even better yield than sugar cane at an experimental French farm.

For ethanol,
the top yields per acre are 714 gallons from sugar beets in France and
662 gallons per acre for sugarcane in Brazil

This might well be misleading as sugar beets are hard on the soil and need to be rotated rather more than other crops. That site mentions that one sugar beet crop per field every 4 years is a good rule of thumb with one per 3 being rather risky, so the number probably would realistically be 1/4th of that given.

By comparison, according to this report, switchgrass yields a theoretical maximum of 1,150 gallons of ethanol per acer.

These numbers are also somewhat as the celulosic process mentioned in the post is not fully operational (though it is very promising). The big advantage of switchgrass is that it is a weed, a native species and can be grown very well on marginal land that isn't really suitable for other crops. This is not the case with sugar beets and is important because we don't want to be displacing food crops for fuel. That is a very bad thing!

I personally think that algael oil, about which more here, here and here is a better option in general with a yield of kerosene type hydrocarbons 50 times that of the best ethanol producing crops. However, switchgrass certainly has potential to supplement that. (Ethanol also works fairly well in suitable Otto cycle engines, whereas algae produces what is fairly close to diesel fuel.)

A comparison of various crop yields can be found here. Note that most displace food and that Congressional favorite corn is by far the worst of the lot.

The reasons for that stem from in part from the anti nuclear hysteria found in so much of the green movement, but also from a policy decision made by the Carter administration in 1977 when we got out of the fuel reprocessing business. The idea was that plutonium should not become a commodity to be traded and that this would ease proliferation risks...In practice this meant the US ceded an entire industry to the Europeans, the Russians and the Japanese.

Additionally, the media has been very hostile to nuclear power in general over the
years. It should be rembered too that this is a technology that was abandoned. This gives, to a casual observer, the
mistaken impression that it failed....which can cause it to be further
dismissed.

The most promising thorium reactors are liquid fluoride reactors which burn up the vast majority of their fuel, far more efficiently and with less ultimate waste than other types. However this cycle is a breeder cycle and that got it nixed from consideration. Other types of thorium plants have the advantage of using thorium fuel instead of uranium of course. This vastly increases global fuel reserves but these other thorium reactors don't really minimize waste as far as I know.

A previous post on this blog regards nuclear power in general can be found here, and nuclear scientist Kirk Soronsen...who actually KNOWS what he's talking about...has a blog as well as a very informative discussion forum where thorium fueled reactor related issues are discussed in great detail by a variety of people far more experienced in them than an undergraduate oceanography major.

Undead science babe has been identified as "Franken Fran" and is a creation of Manga artist Kigetsu Katsuhisa.